[PATCH v1 1/4] qemu: revert latest pSeries NVDIMM design changes

[Daniel Henrique Barboza]

On 9/17/20 7:48 AM, Andrea Bolognani wrote:
> On Mon, 2020-09-14 at 23:42 -0300, Daniel Henrique Barboza wrote:
>> In [1], changes were made to remove the existing auto-alignment
>> for pSeries NVDIMM devices. That design promotes strange situations
>> where the NVDIMM size reported in the domain XML is different
>> from what QEMU is actually using. We removed the auto-alignment
>> and relied on standard size validation.
>>
>> However, this goes against Libvirt design philosophy of not
>> tampering with existing guest behavior, as pointed out by Daniel
>> in [2]. Since we can't know for sure whether there are guests that
>> are relying on the auto-alignment feature to work, the changes
>> made in [1] are a direct violation of this rule.
>>
>> This patch reverts [1] entirely, re-enabling auto-alignment for
>> pSeries NVDIMM as it was before. Changes will be made to ease
>> the limitations of this design without hurting existing
>> guests.
>>
>> This reverts the following commits:
>>
>> - commit 0ee56369c8b4f2f898b6aa1ff1f51ab033be1c02,
>> "qemu_domain.c: change qemuDomainMemoryDeviceAlignSize() return type".
>>
>> - commit 07de813924caf37e535855541c0c1183d9d382e2,
>> "qemu_domain.c: do not auto-align ppc64 NVDIMMs"
>>
>> - commit 0ccceaa57c50e5ee528f7073fa8723afd62b88b7,
>> "qemu_validate.c: add pSeries NVDIMM size alignment validation"
>>
>> - commit 4fa2202d884414ad34d9952e72fb39b1d93c7e14,
>> "qemu_domain.c: make qemuDomainGetMemorySizeAlignment() public"
>>
>> - commit 2d93cbdea9d1b8dbf36bc0ffee6cb73d83d208c7,
>> "Revert "formatdomain.html.in: mention pSeries NVDIMM 'align down' mechanic""
>>
>> [1] https://www.redhat.com/archives/libvir-list/2020-July/msg02010.html
>> [2] https://www.redhat.com/archives/libvir-list/2020-September/msg00572.html
> 
> Reverting multiple commits with a single commit is sort of unusual,
> but in this case it seem to make sense and I don't really have a
> problem with it, so unless someone shouts against this approach I
> think we can merge it as-is.
> 
> A few tweaks to the commit message, though:
> 
>    * keep the order of commits consistent to the one they were merged
>      in, which more specifically means putting 2d93cbdea9d1 at the
>      very top of the list;
> 
>    * lose the commas after the various commit hashes - they break
>      convenient double-click selection in most terminals;
> 
>    * indent the commit subject by two spaces for better readability.

Ok!

> 
> The commit is also missing your S-o-b, and as you know that's a
> blocker for merging.

Ouch. reverting + squashing took its toll ....

> 
> With the above addressed,
> 
>    Reviewed-by: Andrea Bolognani <abologna at redhat.com>
>